Five years ago, I kissed a man who had what I thought was a cold sore on his lip. About two weeks later, I broke out in vaginal sores that were diagnosed as genital herpes. I did not have any sexual contact with this man or any man four years prior to the kiss. I have only had the one outbreak. Is it possible for genital herpes to be transmitted from a kiss, and can herpes tests have false-positive results?

W.

There is widespread confusion regarding herpes infections and how they are transmitted. In case you don't know, there are two viruses that cause herpes -- herpes simplex viruses (HSV) 1 and 2. HSV-2 causes most cases of herpes on the genitals, while HSV-1 causes most cases of oral herpes (on the lips and mouth). However, either virus can cause either illness.

Oral herpes is a common infection, affecting more than half of all Americans. The initial infection usually causes no symptoms, but in some people it can be severe, with fever, intense pain, blisters in the mouth and throat and headaches. HSV is never eradicated from the body, so recurrent infections occur. Fortunately, these recurrences are generally not severe, manifesting mainly as cold sores on the lip, as you describe.

Genital herpes is similar to oral herpes in that the initial infection, if symptomatic, tends to be more severe than recurrences are. In addition to the manifestations I described for severe oral herpes, there can be meningitis (inflammation of the membranes covering the brain and spinal cord) and bladder problems.

HSV-1 and HSV-2 are transmitted by direct contact. That may mean contact with a sore on an infected person, but it may also mean contact with the oral or genital region of an infected person who has no visible sores. Since the virus is spread by direct contact, I would not expect you to acquire genital herpes after only a kiss.

The incubation period (time from infection to the first manifestations of disease) for herpes is usually less than a week. The short incubation period also speaks a bit against you having contracted herpes from the encounter you describe, but incubation periods of two weeks or more have certainly been reported.

There are several possibilities in your case. First, you may not have had herpes at all. A few other conditions can mimic the infection. Laboratory tests can easily prove or disprove the diagnosis. Second, you could have transferred the virus from your mouth (or his mouth) to your genital region. This seems a bit unlikely, but it is certainly possible. Frequently, people will develop herpes infections of the finger after touching lesions on the mouth or genitals. The third -- and I think the most likely -- possibility is that you actually had a recurrence of a genital herpes infection that occurred previously. If you had never had genital lesions before, then your initial infection was asymptomatic. This commonly occurs in genital infection, and it is the most common presentation of oral infections. In other words, the first manifestation of any herpes infection is often a recurrence.

As to your last question, the best way a physician can diagnose a herpes infection is by sending the fluid from a sore to a laboratory for culture (growing any microbes present). Rapid tests are also available for detecting the virus without waiting for it to be cultured in a lab. If your lesions tested positive for herpes either from culture or from one of the newer techniques for viral detection, I would say that you almost certainly had herpes. In rare cases, there can be false-positive tests, but if your physician thought you had herpes, and if one of these tests were positive, then you probably had herpes. On the other hand, blood tests for antibodies against herpes are not as reliable.